: OBJECTIVE: Cerebral small vessel diseases (CSVDs) are common causes of cognitive impairments and mood disorders. In recent years, event-related potential P300 has received increasing attention as a biomarker of cognitive impairments or mood disorders. Previous studies on P300 mainly focused on anxiety, depression or cognitive impairments, and few results have been reported on P300 in CSVD patients. The present study aimed to explore the relationship between neuropsychological test scores and P300 in patients with CSVDs. METHODS: The clinical data of 52 patients with CSVDs admitted to the Neurology ward of the First Hospital of Jilin University from June 2016 to October 2017 were collected. All patients who met the inclusion criteria were assessed by both cognitive tests and mood scales within 1 week after enrollment, followed by measurement of P300. Accordingly, patients were assigned to the following four groups: cognitive impairment, non-cognitive impairment, mood disorder, and non-mood disorder.The amplitude and latency values of P300 were measured from the Pz, Fz, Fpz, C3, C4 and Cz electrode sites. In addition, correlations of P300 responses and neuropsychological test scores were analyzed. RESULTS: Significant differences were found in the P300 latency values between the cognitive impairment group and non-cognitive impairment group (P<0.05). P300 latency values were more significantly prolonged in the mood disorder group at the Fz, C3 and Cz electrode sites than in the non-mood disorder group. Positive correlations were found between Hamilton Depression Scale scores and C3, Fz and Cz latencies. Females tended to have a statistically higher risk of emotional impairment than did males (p<0.05). CONCLUSION: P300 latency values can be used as a objective indicator of cognitive impairments and mood disorders in CSVD patients.